The power characteristics of an engine can be changed by increasing or decreasing the internal rotating mass, which may be commonly referred to as flywheel weight or flywheel inertia. Decreasing the flywheel inertia will cause the engine speed (RPMs) to increase at a quicker rate during acceleration conditions. Such increases in engine speed during acceleration conditions may make drivability or handling of a vehicle (e.g., a motorcycle) more difficult to control. Accordingly, during acceleration conditions, the rider must use more throttle control, concentration, strength, and energy to maintain traction and control of the vehicle.
Increasing the flywheel inertia will make the engine speed increase at a slower rate during acceleration conditions that may make vehicle acceleration easier to control. Since the engine speed increases at a slower rate, engine torque may be transferred to the vehicle's tires at a slower rate that makes the tires less likely to lose traction. Further, the rider has more time to make corrections. Moreover, the increased engine inertia, or engine momentum, may also keep the engine from stalling or dying out. Accordingly, the vehicle may travel at lower engine speeds with less of a possibility of the engine suddenly stalling. In other words, the increase in flywheel inertia allows a rider to “chug” at lower engine speeds with less of a possibility of the engine suddenly stalling.
Thus, for ease of control, some riders prefer to add more weight to their ignition flywheels. One prior approach that has been employed is to bolt on or screw on a steel disc to the existing ignition flywheel, while this approach is easily implemented by an amateur mechanic, it suffers from the drawback that sufficient space must be present within the flywheel case for clearance of the bolt or screw, and the bolt or screw may become loose over time, potentially leading to catastrophic failure at high engine speeds.
Other prior approaches include welding a steel ring to the existing ignition flywheel, pressing on an interference fit metal ring to the flywheel, adding heavy metal to the crankshaft, building a larger or heavier crankshaft, building a larger or heavier ignition flywheel, or building a clutch basket out of heavier material. While each of these approaches increases the rotational mass of the powertrain, most of these methods are too expensive or beyond the engineering capabilities of an amateur mechanic. Although the bolt on/screw on weight disc discussed above is within the technical ability of an amateur mechanic to install, this approach is becoming more difficult to implement because four stroke engines with increasingly compact configurations are becoming more popular in motorcycles as compared to two stroke engines. Since four stroke engines are generally larger, heavier, and have more parts than a two stroke engine of the same displacement, manufacturers are making the four stroke engines more compact, leaving less room to add flywheel weight in the ignition area. Four stroke engines generally have the ignition flywheel in the same oil cavity as the rest of the vital engine parts, so if a fastener comes out of a flywheel weight, damage to the engine can be extensive. In addition, ignition flywheels have generally changed in design, due in part to electronic fuel injection, making it much more difficult to attach a weight disc using fasteners.
For manufacturers of aftermarket flywheel weights, the challenge has been to find an inexpensive and easily implemented way to add more inertia to compact engine and ignition designs.